1. Field
The following description relates to an organic light-emitting diode including a multi-layered hole transporting layer and a flat display device including the organic light-emitting diode.
2. Description of Related Art
Organic light emitting diodes are self-emission devices and enable generation of multi-color images. In addition, the organic light emitting diodes have a wide viewing angle, a high contrast ratio, a short response time, and excellent brightness, driving voltage, and response speed characteristics.
In a typical organic light-emitting diode, an anode is formed on a substrate, and a hole transport layer, an emission layer, an electron transport layer, and a cathode are sequentially formed in this stated order on the anode. In this regard, the hole transport layer, the emission layer, and the electron transport layer are organic films including organic compounds. When a voltage is applied between the anode and the cathode, holes injected from the anode pass through the hole transport layer and migrate toward the emission layer, and electrons injected from the cathode pass through the electron transport layer and migrate toward the emission layer. The holes and electrons, which are carriers, are recombined in the emission layer to generate excitons, and then the excitons change from an excited state to a ground state, thereby generating light.
A hole transport material used in a hole transporting layer has, in general, excellent hole injection function or hole transport function, thereby forming a device with a low driving voltage. That is, if a hole transport material having high hole mobility is used in a hole transporting layer, the driving voltage of the formed device is substantially decreased. However, charges are excessively injected and thus, a formed device may have low efficiency and a short lifespan (lifetime). To resolve these problems, many efforts have been made.